Interface-Mediated Migration of Sperm Cells in Methylcellulose-Based Shear-Thinning Microenvironments for Efficient Separation

Efficient and physiologically relevant separation of motile sperm cells is crucial for improving outcomes in assisted reproductive techniques (ARTs) such as intracytoplasmic sperm injection (ICSI) and in vitro fertilization (IVF). This study presents a simple, cost-effective biomimetic method that replicates the microenvironments of the female reproductive tract (FRT) through the shear-thinning properties of a biopolymer. The method involves placing a semen droplet on a biopolymer droplet, forming fluid interfaces that mimic cervical barriers. Motile sperm actively traverse this interface, while nonmotile sperm remain confined, enabling efficient selection without external pumps or microfluidic components. Comprehensive rheological characterization, sperm kinematic analysis, and high-speed flagellar imaging were performed to establish the underlying mechanism. Furthermore, arbitrary Lagrangian-Eulerian (ALE) simulations were used to elucidate sperm-fluid interactions in shear-thinning media. Results identified 0.5% methylcellulose (MC) as the optimal concentration for enhancing sperm progression with improved straight-line velocity, beat frequency, and progression per flagellar beat. Using this medium, a separated sperm concentration of approximately 0.704 million motile cells per mL was achieved within 15 min from a 5 μL semen sample, demonstrating rapid and efficient motile-sperm separation. The method yielded significantly higher progressive motility (98 ± 1.5%) compared to swim-up (80.3 ± 3.8%), DGC (71.6 ± 7.4%), and raw semen (45.5 ± 4.08%), and substantially reduced the DNA fragmentation index (3.4 ± 1.8%) relative to swim-up (9.8 ± 4.5%), DGC (20.2 ± 7.3%), and raw samples (17.9 ± 5.4%). This integrated biomimetic strategy provides a physiologically relevant and clinically adaptable approach for isolating high-quality sperm, with strong potential for direct incorporation into the ART paradigm.